Tricyclic antidepressants amines

The original monoamine hypothesis of depression states that depressions are associated with a deficiency of catecholamines, particularly norepinephrine, at functionally important adrenergic receptor sites in the brain. Elation conversely may be associated with an excess of such amines. The hypothesis was articulated in 1966 only after the mechanism of action of the tricyclic antidepressant desipramine and of the psychostimulants... 

The main problems with early, irreversible MAOIs were adverse interactions with other drugs (notably sympathomimetics, such as ephedrine, phenylpropanolamine and tricyclic antidepressants) and the infamous "cheese reaction". The cheese reaction is a consequence of accumulation of the dietary and trace amine, tyramine, in noradrenergic neurons when MAO is inhibited. Tyramine, which is found in cheese and certain other foods (particularly fermented food products and dried meats), is normally metabolised by MAO in the gut wall and liver and so little ever reaches the systemic circulation. MAOIs, by inactivating this enzymic shield, enable tyramine to reach the bloodstream and eventually to be taken up by the monoamine transporters on serotonergic and noradrenergic neurons. Fike amphetamine, tyramine reduces the pH gradient across the vesicle membrane which, in turn, causes the vesicular transporter to fail. Transmitter that leaks out of the vesicles into the neuronal cytosol cannot be metabolised because... 

The answer is b. (Katzung, p 499. Hardman, p 4.3.3.) Amitriptyline is a tertiary amine tricyclic antidepressant. It functions as a norepinephrine... 

The linkage of uptake to the Na+ gradient may be of physiological significance since transport temporarily ceases at the time of depolarization-induced release of catecholamines. The transport of catecholamines can be inhibited selectively by such drugs as tricyclic antidepressants and cocaine. In addition, a variety of phenylethyl-amines, such as amphetamine, are substrates for carrier thus, they can be concentrated within catecholamine-containing neurons and can compete with the catecholamines for transport. 

GG is used extensively for analysis of antidepressants (Orsulak et al, 1989), but HPLC assays and enzyme immunoassays have become more popular in recent years. However, GC has advantages such as economy and ready availability. LCD and NPD generally are the detectors of choice (Coutts and Baker, 1982). NPD is relatively efficient for the analysis of tricyclic antidepressants (TCAs) as derivatization is not necessary, although the secondary, demethylated amines are sometimes derivatized to improve resolution and peak shape (Coutts and Baker, 1982). Acetylation, under aqueous or anhydrous conditions, followed by GC-NPD, has been used extensively for analysis of TCAs and the tetracyclic antidepressant maprotiline in plasma samples (Drebit et al., 1988). O Table 1-1 summarizes GC assays for some commonly prescribed antidepressants and their metabolites. 

Tricyclic Antidepressants (TCAs). The TCAs, particularly imipramine (Tofranil), were also discovered soon after their introduction to be effective in the treatment of panic attacks. Imipramine, the best-studied TCA in the treatment of panic disorder, is most often helpful at daily doses of 150-250 mg, though it must be started at 10-25 mg, usually at bedtime, and gradually increased over 2-4 weeks. Although they are not as well studied, many clinicians prefer to use the secondary amine TCAs, desipramine (Norpramin) and nortriptyline (Pamelor), because they have milder side effects than imipramine. Clomipramine (Anafranil), though probably the TCA with the greatest side effect burden, is often said to be most effective in patients with refractory disease. 

Serendipity has played a major role in the discovery of most classes of psychotropic drugs. For example, the observation that the first antidepressants, the tricyclic antidepressants and the monoamine oxidase inhibitors, impeded the reuptake of biogenic amines into brain slices, or inhibited their metabolism, following their acute administration to rats, provided the experimenter with a mechanism that could be easily investigated in vitro. Such methods led to the development of numerous antidepressants that differed in their potency, and to some extent in their side effects (for example, the selective serotonin reuptake inhibitors) but did little to further the development of novel antidepressants showing greater therapeutic efficacy. The accidental discovery of atypical antidepressants such as mianserin led to the broadening of the basis of the animal models... 

Like sertraline, these two drugs are selective serotonin reuptake inhibitors. Fluoxetine is prescribed for depression, bulimic binge-eating and vomiting, obsessive-compulsive disorder, obesity, alcoholism, and anorexia among other ailments. Paroxetine is used for depression and obsessive-compulsive disorder. Interestingly the three top antidepressants are chemically unrelated to each other, except for being amines, and are unrelated to earlier tricyclic antidepressants. 

It is believed that tricyclic antidepressants inhibit the (neuronal) reuptake of norepinephrine (noradrenaline) and/or serotonin by presynaptic nerve endings, thus blocking one of the leading mechanisms of their inactivation, and thereby increasing the concentration of the indicated amines potentiating their effects. It should be noted that, as a rule, secondary amines, which are representatives of tricyclic antidepressants, exhibit high activity, blocking the neuronal reuptake of norepinephrine, while tertiary amines act more on the neuronal reuptake of serotonin. 

Imipramine is the primary representative of typical tricyclic antidepressants. It acts by blocking the mechanism of renptake of biogenic amines. It does not inhibit MAO activity. Imipramine lessens sadness, lethargy, improves mood, and improves the mental and overall tone of the body. It is nsed in depression of varions etiology accompanied by motor cinmsiness and ennresis in children and Parkinson s disease. Primary synonyms of this drag are tofranil, snrplix, imizin, melipramin, and others. 

Pharmacology The tricyclic antidepressants (TCAs), structurally related to the phenothiazine antipsychotic agents, possess 3 major pharmacologic actions in varying degrees Blocking of the amine pump, sedation, and peripheral and central... 

The tricyclic antidepressants (e.g., desipramine and amitriptyline) and some phenothiazines block the sympathetic neuronal amine uptake system they thereby would also block the uptake of guanethidine and thus reduce its hypotensive effectiveness. Conversely, guanethidine competitively inhibits the uptake of drugs that are substrates for neuronal uptake, such as the indirectly acting adrenomimetics, or sympathomimetics (see Chapter 10). 

Equally effective as other tricyclic antidepressants for depression fewer anticholinergic effects than tertiary amines, less orthostasis, and mild stimulatory property... 

Tricyclic antidepressants (TCAs) modulate various brain neurotransmitters, especially norepinephrine and serotonin, by blocking reuptake presynaptically. The secondary amines (desipramine, nortriptyline) are more selective for noradrenergic function and have less side effects in sensitive populations. Advantages of this class of drugs include their relative long half life (approximately 12 hours), absence of abuse potential, and putative positive effects on mood and anxiety, sleep, and tics. 

Reuptake through the presynaptic membrane is the major deactivation mechanism for serotonin. It is prevented by the tricyclic antidepressants (see section 4.3.7), among which the tertiary amines are more potent at serotonergic terminals than are the secondary bases, whereas the reverse is true for catecholaminergic synapses. 

Partly reduced counterparts of the indole nucleus provide the basis for several agents with varied biological activities. A pair of closely related A-phenyl derivatives have both shown antidepressant activity in test systems. The apparent preference for the monomethyl amine suggests that these act by the same mechanism as the classical tricyclic antidepressants, where the secondary amine is the more active species. The first step in the preparation of the common intermediate (27-3) to these compounds consists of acylation of diphenylamine (27-1) with chloroacetyl chloride. 

Tricyclic antidepressants potentiate the pressor effects of directly acting sympathomimetic amines, such as adrenaline (epinephrine) or noradrenaline (norepinephrine), to cause hypertension. Small amounts of these, such as may be present in local anaesthetic solutions, can be dangerous. Tricyclic antidepressants will inhibit the antihypertensive effects of the older anti hypertensive drugs, such as adrenergic neurone-blocking agents, e.g. guanethidine, a-methyl-DOPA, and clonidine. 

A growing number of drugs are used that affect the many neurotransmitters in the brain benzodiazepines and others act on GABAergic transmission antidepressants, such as monoamine oxidase inhibitors and tricyclic antidepressants, are thought to increase the concentration of transmitter amines in the brain and so elevate mood—these will also act at peripheral nerve terminals, so interactions with them are a combination of peripheral and central actions. Levodopa (L-dopa) increases central as well as peripheral dopamine, and the newer class of psychoactive drugs, the selective serotonin reuptake inhibitors (SSRIs) of which the ubiquitous fluoxetine (Prozac) is best known, act in a similar way on serotonergic pathways. 

Many inhibitors of the amine transporters for norepinephrine, dopamine, and serotonin are used clinically. Although specificity is not absolute, some are highly selective for one of the transporters. Many antidepressants, particularly the older tricyclic antidepressants can inhibit norepinephrine and serotonin reuptake to different degrees. This may lead to orthostatic tachycardia as a side effect. Some antidepressants of this class, particularly imipramine, can induce orthostatic hypotension presumably by their clonidine-like effect or by blocking 04 receptors, but the mechanism remains unclear. 

Because neuronal uptake is necessary for the hypotensive activity of guanethidine, drugs that block the catecholamine uptake process or displace amines from the nerve terminal (see Chapter 6) block its effects. These include cocaine, amphetamine, tricyclic antidepressants, phenothiazines, and phenoxybenzamine. 

One of my patients regularly had a ferocious alligator come out from under her bed and snap its teeth at her This unwelcome bed partner only appeared when we were raising, or more commonly lowering, the patient s dose of amytriptyline, a tricyclic antidepressant that blocks the reuptake of the biogenic amines norepinephrine and serotonin (and so potentiates them) and also blocks the action of acetylcholine (and so enfeebles that system). Now that we know that REM sleep dreaming is... 

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